This substrate is very hydrophobic and diluting a concentrated DMSO stock directly in the aqueous medium will cause precipitation on the border between the DMSO drop and the medium. Sometimes it could help to dilute the DMSO stock 1:1 with medium resulting in a 50 % DMSO solution followed by another dilution step 1:1 resulting in 25% solution and so on. It takes more time but it very often works well.

Best MIKE